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COST-EFFECTIVE MITIGATION STRATEGY DEVELOPMENT FOR BUILDING RELATED EARTHQUAKE RISK Annual project report 2017-2018
Griffith
University of Adelaide & Bushfire and Natural Hazards CRC
gabriel.zitoTypewritten Text
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COST-EFFECTIVE MITIGATION STRATEGY DEVELOPMENT FOR BUILDING RELATED EARTHQUAKE RISK | REPORT NO. 464.2019
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Version Release history Date
1.0 Initial release of document 05/03/2019
This work is licensed under a Creative Commons Attribution-Non Commercial 4.0
International Licence.
Disclaimer:
Universities of Adelaide, Melbourne, and Swinburne, Geoscience Australia, and
the Bushfire and Natural Hazards CRC advise that the information contained in this
publication comprises general statements based on scientific research. The
reader is advised and needs to be aware that such information may be
incomplete or unable to be used in any specific situation. No reliance or actions
must therefore be made on that information without seeking prior expert
professional, scientific and technical advice. To the extent permitted by law,
Universities of Adelaide, Melbourne, and Swinburne, Geoscience Australia, and
the Bushfire and Natural Hazards CRC (including its employees and consultants)
exclude all liability to any person for any consequences, including but not limited
to all losses, damages, costs, expenses and any other compensation, arising
directly or indirectly from using this publication (in part or in whole) and any
information or material contained in it.
Publisher:
Bushfire and Natural Hazards CRC
March 2019
Citation: Derakhshan, H., Lumantarna, E., Hing-Ho, T., Wilson, J., Lam, N.T.K.,
Edwards, M., and Griffith, M. C. (2018). “Cost-effective mitigation strategy
development for building-related earthquake risk”. Project A9, 2017-18 Annual
Report. Published by Bushfire and Natural Hazards CRC. Melbourne. Australia.
Cover: Dust clouds of the Feb 2011 Christchurch earthquake (© Gillian
Needham)
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TABLE OF CONTENTS
EXECUTIVE SUMMARY 3
END USER STATEMENT 4
INTRODUCTION 5
WHAT THE PROJECT HAS BEEN UP TO 6
Conference and Workshop Attendance 6
Numerical investigation of accelerations applied on unnreinfored masonry components 6
Study of drift-damage relationships for URM buildings 9
Generalised force method for displacement demand estimates on Irregular buildings 10
Seismic demands on podium-tower buildings 14
Numerical studies to develop Lateral drift model for limited ductile reinforced concrete column 15
Seismic fragility functions for podium-tower buildings 17
Analytical development of seismic retrofit method for limited ductile reinforced concrete beam
to column joint using diagonal metallic haunch 20
Ongoing Research 22
Project Revision – Revised Scope and Going Forward 24
PUBLICATIONS LIST (JULY'17 - JUNE'18) 25
Final Reports 25
book chapters 25
Journal Papers 25
Conference Papers 26
PROJECT TEAM MEMBERS (CRC SUPPORT NOTED IN BRACKETS) 27
Researchers 27
CRC Funded Post-Doc Researchers (1.2 FTE) 27
Students (1.0 FTE) 27
End Users 27
REFERENCES 28
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EXECUTIVE SUMMARY
This annual report contains a summary of 12-month research undertaken by 4
partner institutions towards the development of cost-effective seismic retrofit
methods for vulnerable Australian buildings.
Progress has been made in 3 complementary fronts to:
1) Understand the existing unreinforced masonry (URM) and limited ductile
reinforced concrete (LDRC) building vulnerabilities and methods to
address them through seismic retrofit;
2) Risk assessment of the building stock through development of an
economic loss model; and
3) Advance an end user focused research utilization project in the area of
community risk reduction. This is done through an Earthquake Mitigation
Case Study for the historic town of York in Western Australia.
The first of the above components is being researched in the Universities of
Adelaide, Melbourne, and Swinburne. This work includes investigation of existing
building seismic capacities and development of retrofit techniques. The second
area is being studied by Geoscience and the work includes estimating direct
and indirect losses associated with building damage and benefits from seismic
retrofit. The last component is completed utilizing the research findings in the two
other areas.
Finally, using the new damage loss models and costings for seismically retrofitting
buildings, recommendations are made for the development of seismic retrofit
guidelines and policy based on the strong evidence base developed.
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END USER STATEMENT
Leesa Carson, Geoscience Australia, Commonwealth
During the past 12 months significant progress has been made towards one of
the proposed End User projects. As detailed under “Conference and workshop
attendance”, researchers from GA and Adelaide have been working towards
the WA-based End User program. Some of the engagement activities have
included a travel to York town and:
• Introduction of Department of Fire and Emergency Services (DFES)
personnel to foot survey techniques
• Interview with local newspaper with ensuing article
• Distribution of project flyer through the Council and the York Society to the
public
• Proposed briefing at Australian Earthquake Engineering Society (AEES)
conference tour later in the year
• Preparation and submission of a joint abstract for the upcoming AFAC
conference, with the End User delegates being speakers
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INTRODUCTION
This project arose out of the on-going research efforts by the group involving
structural engineering academics at the Universities of Adelaide, Melbourne and
Swinburne with Geoscience Australia experts all working towards seismic risk
reduction in Australia. Most of the research team are actively involved in the
revision to the Australian Earthquake Loads standard (AS1170.4) as well as being
members of the Australian Earthquake Engineering Society which is a Technical
Society of Engineers Australia. The devastating impact of the 2010 – 11
earthquakes in the Christchurch region on the New Zealand economy and
society has further motivated this group to contribute to this CRC’s aims of risk
reduction for all natural hazards in Australia.
This project addresses the need for an evidence base to inform decision making
on the mitigation of the risk posed by the most vulnerable Australian buildings
subject to earthquakes. While the focus of this project is on buildings, many of
the project outputs will also be relevant for other Australian infrastructure such as
bridges, roads and ports, while at the same time complementing other ‘Natural
Hazards’ CRC project proposals for severe wind and flood.
Earthquake hazard has only been recognized in the design of Australian buildings
since 1995. This failure has resulted in the presence of many buildings that
represent a high risk to property, life and economic activity. These buildings also
contribute to most of the post-disaster emergency management logistics and
community recovery needs following major earthquakes. This vulnerability was
in evidence in the Newcastle Earthquake of 1989, the Kalgoorlie Earthquake of
2010 and with similar building types in the Christchurch earthquake. With an
overall building replacement rate of 2% nationally the legacy of vulnerable
building persists in all cities and predominates in most business districts of lower
growth regional centers.
The two most vulnerable building types that contribute disproportionately to
community risk are unreinforced masonry and low ductility reinforced concrete
frames. The damage to these will not only lead to direct repair costs but also to
injuries and disruption to economic activity.
This research project will draw upon and extend existing research and capability
within both academia and government to develop information that will inform
policy, business and private individuals on their decisions concerning reducing
vulnerability. It will also draw upon New Zealand initiatives that make use of local
planning as an instrument for effecting mitigation.
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WHAT THE PROJECT HAS BEEN UP TO
CONFERENCE AND WORKSHOP ATTENDANCE
BNH CRC Showcase (04 Jul 17) – Mark Edwards presented an overview of the
WA-based End User project and the presentation was followed by a brief
description from Paul Martin, CEO of York Shire Council. The presenters then met
with University of Adelaide researchers through a laboratory tour followed by a
project meeting.
Project workshop 1 (30 Nov 17) – Mark Edwards, Martin Wehner, and Mohanty
Itismita from Geoscience and a number of researchers from University of
Adelaide met in Adelaide in planning for WA End User project works and
engagement programs. Others, who participated via teleconference, were Paul
Martin, CEO of York Shire Council, Stephen Gray (WA DFES), and the media team
from Geoscience.
Project workshop 2 (Dec 17) – Martin Wehner and Mike Griffith travelled to York
in late 2017 planning for WA End User project surveys.
Project activities/workshop 3 (early 2018) - Researchers from Geoscience and
Adelaide travelled to York, WA to meet with several stakeholders including Shire
of York, York Society, York Business Association, DFES, and public (through public
outreach sessions). Project works, including foot survey of buildings and
interrogation of council register of heritage buildings, were completed and
preparations were made for next stages of collaboration including a joint paper
proposal for AFAC 2018.
AFAC’17 (04-06 Sep 17) – Hossein Derakhshan, Alireza Mehdipanah, and Mark
Edwards attended with 3 posters.
AEES17 (24-26 Nov 17) – 5 papers including a Keynote were presented at the
Australian Earthquake Engineering Society (AEES) conference, which was held in
late November in Geoscience Australia (Canberra). The presentations included
a keynote paper by Mike Griffith on performance expectation from Australian
unreinforced masonry buildings.
10AMC (11-14 Feb 18) – One paper was presented on the acceleration response
of unreinforced masonry buildings in the 10th Australasian Masonry Conference,
which was held in Sydney.
NUMERICAL INVESTIGATION OF ACCELERATIONS APPLIED ON UNNREINFORED MASONRY COMPONENTS
A research was undertaken to estimate peak floor acceleration (PFA) for low-rise
URM buildings with flexible diaphragms. These accelerations are applicable to
parts and components that are subject to earthquake movements indirectly
through building shaking. It is important to reliably assess PFA as elevated URM
components pose a significant falling hazard in earthquake. Four building
typologies (Figure 1) were created and analyzed through a parametric study.
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Plan
Plan
In-plane loaded walls of
Building 2
A) BUILDING 1 B) BUILDING 2
Plan
In-plane loaded walls of Building 3
In-plane loaded walls of Building 4
C) BUILDINGS 3 AND 4
FIGURE 1: CASE STUDY BUILDINGS
Several levels of diaphragm in-plane stiffness were assumed in the modelling.
Default material properties for existing timber floors are set out in (ASCE 2014) in
the form of a characteristic shear stiffness, Gd, with a minimum value of
350 kN/m. However, further in situ testing of URM buildings in New Zealand
(Giongo et al. 2014) has suggested values up to a third of this stiffness depending
on the condition (e.g. decay in timber joists) of the diaphragm. A lower bound
of Gd=150 kN/m (D1) was used in this research. As detailed in Table 1, four other
cases of diaphragm stiffness were also studied, including a strengthened timber
floor (D4) and the previously discussed case of rigid diaphragms (represented as
D5 in Table).
Analysis results (Figure 2) shows that for almost all the analysis cases, the PFA to
peak-ground-acceleration (PGA) ratio increases to reach a peak value and
then reduces as the diaphragm becomes increasingly flexible. This effect is more
pronounced for the single-storey buildings. For Building 1, the amplification factor
increased by 175% from 1.2 for diaphragm case D5 (rigid) to a value of 3.3 for the
diaphragm case D2. The PFA in lower floors of the multi-storey buildings is also
affected by diaphragm vibrations as the wall-related vibrations are insignificant
8 9 10 11
E25 E26 E27
E28 E29 E30
n20
n24
N1 N7
N10 N16
N19
N23
15 16 17 18 19
20 21 22 23 24
E49 E50 E51 E52
E53 E54 E55 E56
E57 E58 E59 E60
n28 n30
n31 n33
n34 n36
N1
N7
N13
N19
N22
N25
N29
N32
N35
15 16 17 18 19
20 21 22 23 24
80 81 82 83 84
E49 E50 E51 E52
E53 E54 E55 E56
E57 E58 E59 E60
E95 E96 E97 E98
n28 n30
n31 n33
n34 n36
n55 n57
N1
N7
N19
N22
N13
N46
N25
N52
N29
N32
N35
N56
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due to the first mode shape. Figure 2 also shows the results from a predictive
model that can predict the peak floor acceleration with about 30% error but that
is still under study.
Table1: Range of diaphragm stiffnesses
Designation Description Assumed
Gd, kN/m
Ref. period
Td*, sec
D1 As-built with single straight sheathing 150 1.08
D2 As-built with single diagonal sheathing;
unchorded
600 0.54
D3 As-built with double straight sheathing;
chorded
2400 0.27
D4 Single straight sheathing strengthened with 19
mm plywood overlay with substantial edge
nailing
9600 0.13
D5 Large stiffness representing a rigid diaphragm 3 x 106 0.01
* Calculated using the diaphragm stiffness and the combined mass of the
diaphragm and the tributary mass of the out-of-plane loaded walls (little
variations for different buildings ignored)
a) Roof b) Floors
Figure 2: Peak floor accelerations for buildings with flexible diaphragms
In conclusions, it was found that the peak floor accelerations in buildings with
flexible diaphragms can be up to nearly 2 times greater than that in a building
with rigid floors. Therefore, it is clear that the code approaches (e.g. Australian
seismic loading code, AS1170; AS 2007) that have been developed for ignoring
floor vibrations cannot be applied to buildings that include flexible diaphragms.
0 5 10 15 201
2
3
4
Td/T
1
PF
Aab
s/P
GA
Building 1
0 5 10 151
2
3
4
Td/T
1
PF
Aab
s/P
GA
Building 2
0 2 4 62
3
4
5
6
Td/T
1
PF
Aab
s/P
GA
Building 3
0 1 2 32
3
4
5
6
Td/T
1
PF
Aab
s/P
GA
Building 4
Sa=0.05g
Sa=0.50g
Sa=1.00g
modal
0 50
5
Td/T
1
PF
Aab
s/P
GA
Level 1 - Building 3
0 2 40
2
4
Td/T
1
PF
Aab
s/P
GA
Level 1 - Building 4
0 2 42
4
6
Td/T
1
PF
Aab
s/P
GA
Level 2 - Building 4
Sa=0.05g
Sa=0.50g
Sa=1.00g
modal
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STUDY OF DRIFT-DAMAGE RELATIONSHIPS FOR URM BUILDINGS
The same buildings as shown in Figure 1 were studied to estimate a relationship
between URM building damage and imposed lateral displacements. The
building damage level was represented in 5 increments from D1 (Immediate
Occupancy, IO) to D5 (Collapse). The obtained relationships were compared
and contrasted with the values found in masonry literature including in a
guidelines published by American Society for Civil Engineering (ASCE 2014).
Pushover curves (Figures 3 and 4) were obtained and the condition of the
building damage as reflected in numerical model “damage parameters” were
observed. As part of the utilized numerical technique, masonry walls are
modeled as piers or spandrels and these damage parameters are part of the
material model. Gradual increments in these parameter are an indicative of the
state of shear damage.
a) Building 1 b) Building 2
Figure 3: Pushover curves for Buildings 1 and 2
a) Building 3 b) Building 4
Figure 4: Pushover curves for Buildings 3 and 4
Results are presented in two forms of damage vs. building drift (Table 2) and
damage vs critical storey drift (Table 3).
A direct comparison of the results for ‘critical’ storeys in the 4 studied buildings
with ASCE recommendations suggests that the latter corresponds to a
conservative evaluation of storey drift ratios responsible for different damage
states.
-100 -50 0 50 100
-400
-200
0
200
400
d, mm
V,
kN
-150 -100 -50 0 50 100 150-300
-200
-100
0
100
200
300
d, mm
V,
kN
-150 -100 -50 0 50 100 150-400
-200
0
200
400
d, mm
V,
kN
-200 -100 0 100 200-600
-400
-200
0
200
400
600
d, mm
V,
kN
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The average storey drift ratio that were obtained for damage level D1 are
consistent with the values recommended in ASCE (2014), e.g. 0.23% for D1 vs.
0.30% from Figure 2 for IO limit state.
Larger storey drift ratios were obtained for Collapse Prevention (D4), 2.25% vs. 1%
recommended in ASCE. The drift ratio for intermediate D2 and D3 levels obtained
in this study (0.64% and 1.34%) also exceed ASCE recommendations (0.6% for
D3).
Table 2: Summary of building drift ratios (%) vs damage levels
Building
model
1 2 3 4 Average
(COV)
D1 0.14 0.07 0.26 0.18 0.16
D2 0.71 0.35 0.59 0.44 0.52
D3 1.29 1.18 0.97 0.72 1.04
D4 1.86 1.93 1.29 1.31 1.60
Table 3: Summary of storey drift ratios (%) vs damage levels
Building
model
1 2 3 4 Average for
critical storey
Building
Level
Lvl. 1 Lvl. 1 Lvl.
1
Lvl.
2
Lvl.
1
Lvl.
2
Lvl.
3
---
D1 0.14 0.07 0.5 0.1 0.3 0.2 0.1 0.23
D2 0.71 0.35 1.0 0.2 0.7 0.5 0.2 0.64
D3 1.29 1.18 2.0 0.1 0.8 0.9 0.5 1.34
D4 1.86 1.93 2.7 0.1 1.1 2.5 0.6 2.25
One critical aspect that needs to be addressed in building analysis is the
potentially uneven distribution of structural damage with building height, which
needs to be addressed before expected drifts on URM walls can be determined.
This would not be an issue if the building can indeed be idealised as a SDOF
‘regular’ structure but the definition of structural irregularity is not very well
understood in the context of URM buildings that can have walls with different
thicknesses in different stories.
GENERALISED FORCE METHOD FOR DISPLACEMENT DEMAND ESTIMATES ON IRREGULAR BUILDINGS
Generalised force method has been developed to provide estimates of
displacement demand of multi-storey buildings with vertical irregularities. The
effects of higher modes have been taken into account based on generalised
modal values presented in Figure 5 and by assuming the second modal period
(T2) that is 0.25 of the fundamental natural period (T1) of the building. The values
in Figure 5 are the mean values of results obtained from dynamic analyses
conducted on multi-storey buildings of varying height. The buildings are
supported by reinforced concrete walls and moment resisting frames and
feature vertical irregularities caused by discontinuities of the columns. Several
building configurations with varying contribution of moment resisting frames to
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the lateral stiffness of the building were included in the analyses. Results from the
studies presented in the form of modal values versus normalised height of the
buildings are presented in Figure 6 for the first and second mode of response.
Expressions have been introduced to provide estimates of displacement, inter-
storey drift and inertia forces taking into account the higher modes effects. Figure
8 presents the displacement profile, inter-storey drifts and storey shears for a 20-
storey building (the typical floor is shown in Figure 7). Comparison with results from
dynamic analysis of the building demonstrates that the modified GFM is able to
reasonably estimate the displacement and shear demands on the 20-storey
building.
Figure 5: Generalised modal values (𝑗. 𝑗)
(a) first mode (b) second mode
Figure 6: Modal displacements obtained from parametric studies
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Figure 7: Typical floor plan of the torsionally balanced 20-storey building
(a) Displacement (b) Inter-storey drift
(c) Storey shear
Figure 8: Results from GFM with higher mode effects, 20-storey building
The Generalised Force Method has been extended to provide estimates for
multi-storey buildings with plan irregularities. Expressions have been derived to
0
10
20
30
40
50
60
70
0 10 20 30 40 50 60
he
igh
t (m
)
displacement (mm)
dynamicanalysis
GFM withhigher modeeffects
0
5
10
15
20
0.00% 0.05% 0.10% 0.15% 0.20%
sto
rey
no
.
inter-storey drift
dynamicanalysis
0
5
10
15
20
0 5000 10000 15000
sto
rey
no
.
storey shear (kN)
dynamicanalysis
GFM withhigher modeeffects
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provide estimates of displacement demands at the edges of torsionally
unbalanced buildings with uni-axial and bi-axial asymmetry based on the
following parameters: i) 𝑒𝑥 is the eccentricity perpendicular to the direction of motion; ii) J is the torsional mass of inertia of the TU building; iii) Parameter “b” (=
= √𝐾𝜃 𝐾𝑦⁄ ), which is used to represent the torsional stiffness properties of the TU
building; and iv) a (=𝐾𝑥
𝐾𝑦).
A method to idealise multi-storey buildings with varying storey eccentricity and
stiffness into single storey building model has also been proposed. The method
requires determining the value of the eccentricity exr and that of the torsional
stiffness parameter 𝑏𝑟 noting that the dynamic torsional response behaviour of the building models are characterised by these two parameters. The expressions
based on the values of the torsion parameters can be used to determine the
amplification factors which are applied to the floor displacements to provide
estimates of the maximum displacement demands of the TU multi-storey
buildings. Figure 10 presents comparison between results from GFM and dynamic
analyses of uni-axial and bi-axial asymmetric buildings. The typical plan view of
the building is presented in Figure 9. The comparison shows that the method is
able to approximate the maximum displacement demand of the torsionally
unbalanced buildings.
(a) uni-axial asymmetric building (b) bi-axial asymmetric building
Figure 9: Typical floor plan of torsionally balanced buildings
(a) uni-axial asymmetric building (b) bi-axial asymmetric building
Figure 10: Comparison between GFM and results from dynamic analyses
0
5
10
15
20
25
0 10 20 30 40 50
hei
ght
(m)
displacement (mm)
GFM
DynamicAnalysis
0
5
10
15
20
25
0 10 20 30 40 50
hei
ght
(m)
displacement (mm)
GFM
DynamicAnalysis
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SEISMIC DEMANDS ON PODIUM-TOWER BUILDINGS
Studies have been conducted to investigate the seismic demands of high-rise
buildings with a transfer structure (Figure 11). An analytical procedure for
predicting the increase in shear demands on the tower walls after the supporting
transfer level has been proposed. The shear force increases are the result of the
significant strutting forces (FSTRUT) developed in the slabs (and beams) connecting
adjacent tower walls. Expressions for the strutting force (FSTRUT) as illustrated in
Figure 12 have been proposed as a function of the differential rotation of the
adjacent tower walls about at their bases, the Flexibility Index (FI) and the the differential rotation of the adjacent tower walls about at their bases (TP). The
Flexibility Index (FI) has been defined as a function of the stiffness of the transfer structure relative to the tower walls stiffness. The differential wall rotation TP
correlates with the angle of drift of the building at mid-height. A 2DOF model of
the building tower provided predictions of Peak Rotational Demand (PRD) which can be taken as a conservative estimate of TP. The value of FSTRUT may then be
expressed as the product of FI, PRD and 𝐄𝐂𝐀𝐞𝐟𝐟 𝐰𝐡𝐢𝐜𝐡 𝐢𝐬 the axial stiffness of the connecting elements.
Figure 11: 2D model of the building featuring a transfer plate
Figure 12: Introducing FSTRUT, εSTRUT and ∆θTP, where ∆θTP = θTP1- θTP2
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Three dimensional dynamic analyses were conducted on a building featuring a
transfer structure, as shown in Figure 13. Figure 14 presents the shear force
distribution on the tower walls 1 and 2 showing an increase in the shear demands
at the storey just above transfer force level (indicated by the red line). It is shown
that the sharp increase in shear force on the tower walls above TFL was found to
be of the order of 500 kN (as shown in Figure 14). The results from dynamic analysis
is in good agreement with the prediction of 557 kN made by the proposed
simplified method.
(a) Elevation view of the case study building
showing the analysed walls
(b) 3D render of the FE
model of the case
study building
Figure 13: Case study building
Figure 14: Shear force distribution above TFL from dynamic analyses
NUMERICAL STUDIES TO DEVELOP LATERAL DRIFT MODEL FOR LIMITED DUCTILE REINFORCED CONCRETE COLUMN
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Studies have been undertaken to present a detailed lateral load-drift model
(pushover curve) that possesses the ability to predict the lateral load-drift
behaviour of limited to moderately ductile NSRC as well as HSRC columns.
A detailed lateral load-drift model for RC columns has been proposed, the model
is defined by five points, namely, cracking strength, yield strength, ultimate
strength, lateral load failure (20% lateral strength degradation) and axial load
failure (50% lateral strength degradation) as shown in Figure 15. The model
presented includes the expressions for post-peak failure drift that are applicable
to both NSRC and HSRC columns. Expressions defining each of point have been
developed and calibrated using an extensive database of NSRC and HSRC
columns from the literature. These expressions fit the experimental data very well
and relate the post-peak drift capacity with the following design parameters:
axial load ratio, transverse reinforcement ratio, transverse reinforcement yield
strength and concrete compressive strength.
Figure 15: Detailed lateral load-drift model for RC columns
The model is used to plot pushover curve for a cantilever column of 500×500 mm
cross-section, having an aspect ratio of 4.0 and reinforced with 8N24 longitudinal
bars (v=1.45%). The 3-legged N10 ligatures with a transverse reinforcement yield
strength of 𝑓𝑦ℎ =500 MPa are spaced at 250 mm to give a transverse
reinforcement ratio by area of h=0.19%. The variable parameters for this case
study are concrete compressive strength: 𝑓𝑐′=25 to 𝑓𝑐
′=100 MPa and axial load
ratio: n=0.1 to n=0.4. Results are presented in Figure 16 highlighting the significant
impact of the axial load ratio on the post-peak drift capacity of the RC column.
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(a) (b)
(c) (d)
Figure 16: Lateral load-drift curves for case study example
SEISMIC FRAGILITY FUNCTIONS FOR PODIUM-TOWER BUILDINGS
Fragility curves have been constructed on two groups of building models. The
first group comprises two buildings that feature a setback in the floor plan above
the podium level (buildings designated by SB-1 and SB-2) as shown in Figure 17.
The second group includes two building models incorporating a transfer plate at
the level of the podium (designated by TS-1 and TS-2) as shown in Figure 18. For
all 2D sub-frame models, the tower structure comprises of three walls connected
by floor slabs.
The fragility curves were constructed based on incremental dynamic analyses
using a suite of 40 ground motion records consisting of artificial and historical
records. Scalable intensity measures (IM) of RSDmax, PGV and PGA were
selected to quantify the intensity of the ground motion demand on the building.
The parameter RSDmax is the maximum ordinate of the displacement spectrum of
the ground motion record. The parameter PGA is the maximum value of the
ground acceleration time trace and PGV is the maximum value of the ground
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velocities. The maximum inter-storey drift (ISD) is a common choice for the
engineering demand parameter (EDP) in tall buildings and has been extensively
used to evaluate seismic damages on shear-critical walls and non-structural
components in the building. In this study, the EDP has been specified as the
maximum inter-storey drift ratios (ISD) occurring above the transfer floor or the
podium interface levels. This choice of the EDP with the main focus on the storeys
above the level of the interface is founded on the observations reported that
most of the critical seismic damages have been reported in the storeys above
(and not below) the level of the podium.
Figure 17: Elevation view of the buildings SB-1 and SB-2
Figure 18: Elevation view of the buildings SB-1 and SB-2
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Three performance levels have been considered in this study and these are the
immediate occupancy (IO), Life safety (LS), and collapse prevention (CP) limit
state. The limit for each level is presented in Table 4.
TABLE 4: PERFORMANCE LEVELS ADOPTED
Performance
level Limit
IO/First
indication of
yielding.
ISD corresponding to the first occurrence of flexural
yielding in the RC walls making up the building (in the
tower or the podium).
LS
Life safety limit state is defined as the ISD corresponding
to:
1- Flexural yielding of all the tower walls above the
podium interface level (or TFL)
2- Onset of nominal shear force capacity in the tower
walls
3- Flexural yielding of the transfer plate (in building
models TS-1 and TS-2)
Whichever occurs first
CP
Collapse prevention limit state is defined as the ISD
corresponding to
1. Onset of crushing compression strain in the
confined core of the RC tower walls εcu = −0.003
2. 50% loss of lateral strength in the tower walls (Walls
1 & 2)
3. Onset of nominal shear strength capacity of the
central wall (ultimate strength)
4. Onset of ultimate tensile strain (εsu = 0.03) in the
reinforcement.
Whichever occurs first
Fragility curves are developed following the Multiple Stripe Analysis (MSA)
technique by maximising the likelihood for a limit state to be exceeded. Fragility
curves for the four building models are presented in Figure 19.
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Figure 19: Fragility curves of the building models derived using RSDmax, PGV
and PGA as the IM
ANALYTICAL DEVELOPMENT OF SEISMIC RETROFIT METHOD FOR LIMITED DUCTILE REINFORCED CONCRETE BEAM TO COLUMN JOINT USING DIAGONAL METALLIC HAUNCH
Analytical model has been developed for retrofitting RC exterior beam-column
joint with single haunch element as shown In Figure 20. A single diagonal metallic
haunch was proposed to reduce the shear demand at the exterior beam-
column joint as Illustrated in Figure 21. Expressions have been developed to
compute the shear demand at the joint based on the shear transferring factor,
β. The β factor has been derived by Zabihi et al. (2016a; b) considering both
beam and column deformations.
Figure 20: External actions on exterior beam-column joint: (a) Non-Retrofitted
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System (NRS); and (b) Single Haunch Retrofitting System (SHRS).
Figure 21: Shear force diagrams: (a) Non-Retrofitted System (NRS); and (b) Single
Haunch Retrofitting System (SHRS).
A full scale three-storey RC moment resisting frame has been used as a case
study. The frame has been designed based on the requirements in the 1980’s (as
shown in Figure 22). The frame is 9 m tall, 10 m wide, and is located on a deep or
very soft soil site (i.e. Class D or E as defined in AS1170.4-2007) in Melbourne. The
seismic weight was calculated by assuming 10 kPa gravity loads for all three
levels including dead loads and 30% of imposed loads.
Figure 22: Geometry of case study model: (a) Full-scale RC moment resisting
frame; (b) Exterior Beam-Column Joint; (c) Column section; (d) Beam section.
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The limiting base shear force due to different failure mechanism is plotted in
Figure 23 against the length of haunch. The non-retrofitted subassemblies (NRS)
fails at a base shear level of 286 kN due to the formation of undesirable shear
hinge at the joint zone. By applying a single diagonal haunch (SHRS) with 400 mm
length and at an angle of 45 degrees to the beam, formation of the shear hinge
is shifted from 286 kN base shear level to 339 kN. Although the retrofitted joint can
resist against a stronger earthquake with 18% higher base shear force, the joint
will still fail at the joint zone first which is considered undesirable from the
perspective of capacity design principle. When the single diagonal haunch with
the same angle but longer than 483 mm, a more favourable yielding mechanism,
i.e. beam flexural yielding, will occur.
Figure 23: Strength hierarchy of the exterior beam-column joint subassembly
before and after retrofit
ONGOING RESEARCH
A summary of the research undertaken over the previous year is outlined below.
A team of delegates from Adelaide and Geoscience Australia traveled to
York, WA to make progress on the End User project "Earthquake Mitigation
Case Studies for WA Regional Towns". The activities included:
o Meetings with Shire of York, York Society, York Business Association
o Two public outreach sessions in York
o Foot survey of York road bridges
o Digitisation of council register of heritage listed buildings in York
o RICS survey of York buildings (approximately 1830 buildings)
50
60
70
80
90
100
110
120
130
140
250
300
350
400
450
500
550
600
650
700
400 500 600 700 800
Co
lum
n S
he
ar, V
c[k
N]
To
tal B
ase
Sh
ea
r, V
Ba
se
[kN
]
Length of haunch, Lh [mm]
Joint Shear-Peak LoadBeam-Flexural StrengthColumn-Flexural StrengthBeam-Shear StrengthColumn-Shear Strength
NRS-Ultimate Strength-Joint Failure 50
60
70
80
90
100
110
120
130
140
250
300
350
400
450
500
550
600
650
700
400 500 600 700 800
Co
lum
n S
he
ar, V
c [k
N]
To
tal B
ase
Sh
ea
r, V
Ba
se
[kN
]
Length of haunch, Lh [mm]
NRSUltimate Strength
Joint Failure
SHRSUltimate Strength
Joint Failure
SHRSUltimate Strength
Beam Failure
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o Foot survey of old non-residential URM buildings in York
(approximately 50 buildings)
o Foot survey of York businesses (approximately 75 businesses)
o Detail survey of three buildings (St Patricks Church, Convent, Town
Hall)
o Digitisation of survey records ( in progress)
o Engagement with end users
GA has prepared a building schema that categorises the Australian building
stock into classes with distinctly different vulnerabilities to earthquake. The
schema will enable the case studies undertaken later in the project to assign
vulnerability functions developed by the project to buildings.
Research in ongoing to produce URM building fragility curves for the non-
structural URM building components. Significant research has been
undertaken by University of Auckland by collecting empirical data from the
2010-2011 Canterbury earthquake swarm. This information will be
supplemented by analyses of more scenarios to generate fragility curves that
would be one of the deliverables in the second phase of Project A9.
Experimental work into the durability of seismic retrofit of masonry elements is
ongoing. FRP-strengthened specimens were subjected to environmental
condition since the 2nd quarter of 2014-2015 and tested at different
milestones of 6 months, 1 year, and 18 months. The last testing stage (24
months) is to be completed in the next few weeks.
Experimental testing of high-strength RC columns under uni-directional and
bi-directional cyclic load is on-going to validate numerically developed
latera drift relationship for limited ductility reinforced concrete columns.
Studies on different retrofitting options for limited ductility reinforced concrete
buildings are ongoing.
Preparation is well underway on experimental testing of axial stiffness of
anchor groups in concrete as part of the haunch retrofit system for reinforced
concrete beam-column joint. Numerical investigation is ongoing on the
impact of haunch retrofit system on the seismic performance of limited
ductile reinforced concrete frames.
Numerical studies are currently underway to investigate the impact of the
minimum requirement for the design hazard factor 0.08 g on the seismic
design and performance of limited ductile reinforced concrete buildings. The
potential impacts of designing buildings for lower annual probability of
exceedance were also explored.
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PROJECT REVISION – REVISED SCOPE AND GOING FORWARD
Earthquake Mitigation Case Studies for a WA Regional Town:
This End User is well engaged and scope revision has not been necessary. The
project is well on track with significant desktop and site works already completed.
Results from site inspections and building typology study that were completed in
in early 2018 are planned to be augmented to the building exposure data
available from NEXIS in a follow-up desktop study. In the next few months,
heritage-sensitive choices of seismic retrofit methods will be
developed/formulated and costing that will provide the basis for cost-benefit
analysis will be undertaken. End user demonstration of seismic retrofit methods is
currently being planned on buildings that are scheduled for demolition.
Holistic Risk Assessment of Regulatory Requirements for Earthquake Design:
This proposed End User project did not go ahead.
Rapid Visual Screening (RVS) Procedure
This proposed End User project did not go ahead.
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PUBLICATIONS LIST (JULY'17 - JUNE'18)
Note - only those published between 1 July 2017 & 30 June 2018 and has CRC in acknowledgments are listed.
FINAL REPORTS Mohanty, I., Edwards, M., Hyeuk, R., Wehner, M. (2018). “Final report on business
resilience models”. Submitted to Bushfire and Natural Hazards CRC (February 2018). Melbourne. Australia.
Lumantarna, E., Tsang, H.H. (2017). “Final report on limited ductile reinforced concrete buildings drift-damage relationships”. Published by Bushfire and Natural Hazards CRC (October 2017). Melbourne. Australia.
Lumantarna, E., Tsang, H.H., Goldsworthy, H., Lam, N., Gad, E., and Wilson, J. (2018). “Final report on fragility curves for limited ductile reinforced concrete buildings”. Submitted to Bushfire and Natural Hazards CRC (February 2018). Melbourne. Australia.
Derakhshan, H., Griffith, M. (2018). “Final Report on drift-damage relationships for unreinforced masonry buildings”. Submitted to Bushfire and Natural Hazards CRC (February 2018). Melbourne. Australia.
Derakhshan, H., Griffith, M. (2018). “Final Report on fragility curves for unreinforced masonry buildings”. Submitted to Bushfire and Natural Hazards CRC (June 2018). Melbourne. Australia.
BOOK CHAPTERS Lumantarna, E., Mehdipanah, A., Lam, N., Wilson, J. (2018), Chapter 4, Structural
Analysis, in Guideline on Design of Buildings and Structures in Low-to-Moderate Seismicity Countries, CNERC.
JOURNAL PAPERS Derakhshan, H., Lucas, W., Visintin, P., Griffith, M. C. (2018). "Laboratory testing of
strengthened unreinforced clay brick masonry cavity walls", Journal of Structural Engineering, 144(3), 04018005, DOI: 10.1061/(ASCE)ST.1943-541X.0001987.
Derakhshan, H., Lucas, W., Visintin, P., Griffith, M. C. (2018). "Out-of-plane strength of existing two-way spanning solid and cavity unreinforced masonry walls", Structures (Elsevier), 13, pp. 88-101, DOI: 10.1016/j.istruc.2017.11.002.
Derakhshan, H., Visintin, P., Griffith, M. C. (2017). "Case studies of material properties of late nineteenth-century unreinforced masonry buildings in Adelaide", Australian Journal of Civil Engineering, DOI: 10.1080/14488353.2017.1401196.
Derakhshan, H., Lucas, W., Griffith, M. C. (2017). "In-situ seismic verification of non-structural components of unreinforced masonry buildings", Australian Journal of Structural Engineering, DOI: 10.1080/13287982.2017.1370963.
Hoult, R. D., Goldsworthy, H. M., & Lumantarna, E. (2018). Plastic hinge length for lightly reinforced C-shaped concrete walls. Journal of Earthquake Engineering, 1-32.
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Hoult, R. D., Goldsworthy, H. M., & Lumantarna, E. (2018). Plastic hinge analysis for lightly reinforced and unconfined concrete structural walls. Bulletin of Earthquake Engineering, 1-36.
Yacoubian, M., Lam, N., Lumantarna, E., & Wilson, J. L. (2017). Effects of podium interference on shear force distributions in tower walls supporting tall buildings. Engineering Structures, 148, 639-659.
Yacoubian, M., Lam, N., Lumantarna, E., & Wilson, J. L. (2017). Analytical modelling of podium interference on tower walls in buildings. Australian Journal of Structural Engineering, 18(4), 238-253.
Raza, S., Tsang, H. H., & Wilson, J. L. (2018). Unified models for post-peak failure drifts of normal-and high-strength RC columns. Magazine of Concrete Research, 1-21.
CONFERENCE PAPERS Derakhshan, H., Nakamura, Y., Goldsworthy, H., Walsh, K.Q., Ingham, J.M., and Griffith,
M.C. (2018). “Peak floor accelerations in unreinforced masonry buildings with flexible diaphragm”, 10th Australasian Masonry Conference (10AMC), 11-14 February, Sydney.
Griffith, M.C., Derakhshan, H., Vaculik, J., Giaretton, M., Dizhur, D., Ingham, J. M. (2017). “Seismic Performance Expectations for Australian Unreinforced Masonry Buildings”, Australian Earthquake Engineering Society (AEES) Conference, 24-26 November, Canberra.
Hoult, R. D., Goldsworthy, H. M., & Lumantarna, E. (2017). Seismic performance of lightly reinforced and unconfined c-shaped walls. In Australian Earthquake Engineering Society 2017 Conference.
Hoult, R. D., Goldsworthy, H. M., & Lumantarna, E. (2017). Seismic Assessment of the RC building stock of Melbourne from rare and very rare earthquake events. In Australian Earthquake Engineering Society 2017 Conference.
Amirsardari, A., Goldsworthy, H. M., Lumantarna, E., & Rajeev, P. Seismic fragility curves for limited ductile RC Buildings including the response of gravity frames. In Australian Earthquake Engineering Society 2017 Conference.
Mehdipanah, A., Lumantarna, E., & Lam, N. T. Methods of Structural Analysis of Buildings Incorporating Higher Modes Effects. In Australian Earthquake Engineering Society 2017 Conference.
Lumantarna, E., Mehdipanah, A., Lam, N., Wilson, J. (2017), “Methods of structural analysis of buildings in regions of low to moderate seismicity”, 2017 World Congress on Advances in Structural Engineering and Mechanics, Seoul, Korea.
Yacoubian, M., Lam, N., Lumantarna, E., (2017), “Simplified design checks of buildings with a transfer structure in regions of lower seismicity”, 2017 World Congress on Advances in Structural Engineering and Mechanics, Seoul, Korea.
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PROJECT TEAM MEMBERS (CRC SUPPORT NOTED IN BRACKETS)
RESEARCHERS
University of Adelaide: Prof M Griffith (Project Leader), Prof M Jaksa, Assoc
Prof AH Sheikh, Dr MMS Ali, Dr A Ng, Dr P Visintin
University of Melbourne: Prof NTK Lam
Swinburne University: Prof J Wilson, Prof E Gad, Dr HH Tsang
Geoscience Australia: Mr M Edwards, Dr H Ryu, Mr M. Wehner
CRC FUNDED POST-DOC RESEARCHERS (1.2 FTE)
University of Adelaide: Dr Hossein Derakhshan
University of Melbourne: Dr E Lumantarna
STUDENTS (1.0 FTE)
University of Adelaide:
Bambang Setiawan: Quantifying the Seismic and Site Amplification
Characteristics of Adelaide’s Regolith
Yunita Idris: FRP retrofit of non-ductile RC columns
University of Melbourne:
Ryan Hoult: Seismic assessment of reinforced concrete walls in Australia
Anita Amirsardari: Seismic assessment of reinforced concrete buildings in
Australia including the response of gravity frames
Mehair Yacoubian: Effects of Podium Interferences on Seismic Shear Demands in Tower Walls Supporting Buildings
Alireza Mehdipanah: Buildings featuring irregularities in the gravity load
carrying frames in low-to-moderate seismic regions
Bin Xing: Seismic retrofit options for limited ductility RC buildings
Swinburne University:
Scott Menegon: Seismic collapse behaviour of non-ductile RC walls
Yassamin K Faiud Al-Ogaidi: FRP retrofit for non-ductile RC frames
Alireza Zabihi: Seismic retrofit of RC beam-column joints
Saim Raza: Collapse behavior of high-strength reinforced concrete
columns in low to moderate seismic regions
END USERS
Leesa Carson (Geoscience Australia), Ralph Smith (WA)
https://minerva-access.unimelb.edu.au/handle/11343/192443
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REFERENCES
1. ASCE [American Society of Civil Engineers] (2014). Seismic evaluation and
retrofit of existing buildings. ASCE 41-13, Reston, Virginia.
2. AS [Australian Standards] (2007). AS 1170.4-2007 Structural design actions, Part
4: Earthquake actions in Australia. Sydney: Standards Australia.
3. Zabihi, A. et al., 2016a. Analytical development of seismic retrofit technique
for RC beam-column joint using single diagonal haunch. In Mechanics of
Structures and Materials: Advancements and Challenges. CRC Press, pp.
1687–1692.
4. Zabihi, A. et al., 2016b. Retrofitting RC beam-column joint in Australia using
single diagonal haunch. In 2016 Australian Earthquake Engineering Society’s
(AEES) annual conference.
multi peeps logoProject A9 Cost-Effective Mitigation Strategy Development for Building Related Earthquake Risk Annual Report 2017-2018